Synthesis, spectroscopic characterization, thermal stability and biological studies of mixed ligand complexes of gemifloxacin drug and 2,2 0 -bipyridine with some transition metals Sadeek A. Sadeek 1 • Sherif M. Abd El-Hamid 1 • Walaa H. El-Shwiniy 1 Received: 14 June 2015 / Accepted: 3 August 2015 / Published online: 18 August 2015 Ó Springer Science+Business Media Dordrecht 2015 Abstract The mixed ligand Zn(II), Zr(IV), Pd(II), Ce(IV), Th(IV), and U(VI) complexes of gemifloxacin and N-donor 2,2 0 -bipyridine have been prepared. These complexes have been characterized by elemental, infrared (IR), ultraviolet–visible (UV–Vis), 1 H nuclear magnetic resonance (NMR), mass spectroscopy, thermal, molar conductance and magnetic susceptibility analyses. The infrared spectra indicate that gemifloxacin acts as a bidentate deprotonated ligand bound to the metal through the pyridone oxygen and one carboxylate oxygen, whereas the 2,2 0 -bipyr- idine coordinates through the two nitrogen atoms. The central metal in each com- plex is six-coordinate and a slightly distorted octahedral geometry is proposed. The calculated bond length and force constant, F(U=O), in the uranyl complex are 1.751 A ˚ and 641.04 N m -1 , respectively. The thermodynamic parameters are cal- culated from the thermal analysis curves using the Coats–Redfern and Horowitz– Metzger methods. The antibacterial and antifungal activities of the ligand, metal salt and metal complexes have been tested. The data show that the complexes exhibit significant action against some of the four bacterial species but no effect on two species of fungi compared with gemifloxacin. The antitumor activity of the ligands and their complexes has been evaluated against breast (MCF-7) and colon (HCT-116) cancer cells. Keywords Gemifloxacin  2,2 0 -Bipyridine  1 H NMR  Thermal  Cytotoxicity Electronic supplementary material The online version of this article (doi:10.1007/s11164-015-2205-0) contains supplementary material, which is available to authorized users. & Sadeek A. Sadeek s_sadeek@zu.edu.eg 1 Department of Chemistry, Faculty of Science, Zagazig University, Zagazig, Egypt 123 Res Chem Intermed (2016) 42:3183–3208 DOI 10.1007/s11164-015-2205-0